1. Field of the Invention
The present invention relates to a focal plane shutter, a photographing apparatus including the same, and a photographing method for the photographing apparatus, and more particularly, to a focal plane shutter, which can offer a live view function and improve a control velocity of a shutter speed to reduce a time interval between shootings, a photographing apparatus including the focal plane shutter, and a photographing method for the photographing apparatus.
2. Description of the Related Art
The rapid progress in electronics, computers, and the semiconductor technology has changed our daily lives. Personal computers (PCs), which are connected to the Internet and provide various content services, such as community, chatting, games, shopping, and news, are widely used in homes, schools, and offices. Not long ago, the most common way to see photographs was to take the film to a photo processor who would develop a film and print the photographs. With the rapid development in the semiconductor industry digital cameras were commercially introduced.
Digital cameras using a charge coupled device (CCD), which is a semiconductor device, instead of a film are largely available, and mobile communication terminals are also equipped with digital cameras therein. Since digital cameras convert an image into data representing logic (e.g., 0 and 1), digital cameras can provide high robustness against noise, produce high quality signals at low cost, easily process information, compress information like an MPEG audio layer-3 (MP3), joint photographic coding experts group (JPEG), and moving picture experts group (MPEG), and reduce the size of a recording medium.
Digital cameras can be roughly divided into rangefinder cameras and lens reflex cameras.
Rangefinder cameras have a viewfinder in addition to a lens to look through to compose an image. Most of the current autofocus compact cameras and consumer-grade digital cameras are rangefinder cameras in which rangefinders (e.g., a pair of rangefinders) are used to focus a picture.
A rangefinder, which measures a distance to a subject by eliminating parallax, has been used for artillery to measure a distance. When a camera is not focused, two images appear at the center of a viewfinder. Accordingly, the camera is focused by turning a lens rangefinder until the two images are perfectly superimposed. In general, the viewfinder is disposed over a left side of the lens. Because the viewfinder and the lens are placed at different positions, an apparent displacement of the subject occurs, i.e., parallax, as seen from the viewfinder and the lens. Since parallax increases as the subject approaches the camera, parallax correction is necessary when shooting close-up photographs. Since a rangefinder camera has a simple structure without using a mirror and employs a lens shutter, vibration and noise are low during shooting. Since the rangefinder camera has no mirror shock like a single lens reflex (SLR) camera, there is no risk of shaking the rangefinder camera. However, since a lens shutter is employed, the rangefinder camera does not have lens interchangeability, and has an iris and a shutter speed that are more limited than those of the SLR camera.
Lens reflex cameras can be roughly divided into SLR cameras and twin lens reflex cameras. A conventional SLR camera 1, which uses a mirror 20 to reflect an image incident through a lens 10 to a finder screen 34 and a viewfinder 40 to see the image, is shown in FIGS. 1 and 2.
Most of the processional-grade cameras are SLR cameras. FIG. 1 is a cross-sectional view of the conventional SLR camera 1 before a shutter is operated. FIG. 2 is a cross-sectional view of the conventional SLR camera 1 after the shutter is operated. Referring to FIG. 1, an image introduced through the lens 10 of the conventional SLR camera 1 is reflected by the mirror 20 to the finder screen 34, passes through a first objective lens 12, is deviated by a pentaprism 32 by 90° to a second objective lens 14 and a third objective lens 16, and is seen through the viewfinder 40.
The pentaprism 32 is a five-sided reflecting prism that reflects light several times therein and transmits the light through a right angle without inverting it. Since a plurality of optical elements, namely prisms and mirrors, are used in the conventional SLR camera 1, the conventional SLR camera 1 is bulky and heavy.
When the shutter is operated to photograph an image, the mirror 20, disposed in front of an image pickup device 26, is raised to allow an image incident through the lens 10 to enter the image pickup device 26.
In general, the image pickup device 26 is a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). The shutter 24, which is disposed in front of the image pickup device 26 and passes light for a predetermined period of time, is also called a focal plane shutter.
In general, a focal plane shutter is a horizontal or vertical travel shutter which usually includes two cloths or metal curtains installed in front of a focal surface of a lens and allows a photosensitive material to be exposed to a proper amount of light by controlling a slit between a front curtain and a rear curtain or the speed of travel of the front curtain and the rear curtain. Focal plane shutters are widely used in cameras requiring the use of interchangeable lenses such as, for example SLR cameras.
In particular, focal plane shutters are often used in cameras with a format of 6×6 cm or less. Focal plane shutters determine an exposure time by adjusting the width of a slit using a speed regulator or an electrically controlled electromagnet while maintaining a shutter blind speed constant. Focal plane shutters allow for use of interchangeable lenses and enable high speed photographing.
Since the conventional SLR camera 1 can interchange the lens 10 or other lens designed exclusively for digital cameras, the conventional SLR camera 1 can selectively use lenses according to a preference or objective of a user. Also, since the image pickup device 26 is much bigger than that of other conventional digital cameras, noise can be prevented under low illumination conditions and a more precise image can be captured.
However, since the mirror 20 is located to cover the image pickup device 26, an image cannot be seen on a liquid crystal display (LCD) 28 during shooting such that a live view (also known as a preview) function is not offered and only an image review on the LCD 28 of the conventional SLR camera 1 is possible after taking a picture. That is, since an image should be seen through the optical viewfinder 40, the field of view is limited and scenes at various angles including a low angle and a high angle are hidden. Also, when a subject, which is sensitive to any action, should be looked at furtively for a long time and instantaneously photographed, the conventional SLR camera 1 becomes inconvenient because the user must view the subject through the optical viewfinder 40 and because the camera 1 is too heavy to hold for a long time in the same position.
Also, even when a conventional SLR camera 1 can offer a live view function, since a release time lag between the depression of a release button and the commencement of the movement of the shutter is long, an optimal shooting chance is gone and the release time lag is long.